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At least 253 records · Page 14Linked to original sources
PubMed2000

Spatial distribution functions as a tool in the analysis of ribonucleic acids hydration--molecular dynamics studies.

The spatial distribution functions (SDFs) determined as three-dimensional density distribution of hydrogen and oxygen atoms of water in a local coordinate system linked with RNA molecule are used to study details of the spatial structure of aqueous solution around selected parts of RNA duplexes: r(CGCGCG)2 and 2'-O-Me(CGCGCG)2. The influence of the 2'-O-methylation on the hydration pattern of RNA helical fragments is visualized at the atomic level.

Base Pairing↗
PubMed2000

Phylogenetic study of the spatial distribution of protein-coding and control segments in DNA chains.

We examine the size and spatial distributions of the protein-coding and control segments of genes in DNA nucleotide sequences from GenBank. Phylogenetic analysis of these data suggests the presence of spatial order in sequences of higher organisms, irrespective of the nature of nucleotide base content. This is characterized by defined two-point correlation functions and measured by fractal dimensions and singularity spectrum.

Algorithms↗
PubMed2001

Seasonal activity and spatial distribution of host-seeking adults of the tick Dermacentor variabilis.

The seasonal temporal and spatial distribution and emergence of overwintering and summer cohorts of host-seeking American dog tick, Dermacentor variabilis (Say) (Acari: Ixodidae), adults were examined for 5 years in the Bluegrass region of Kentucky. Weekly drag cloth sampling was conducted from early March until late September 1992-1995 and early March until the end of May 1996. Overwintering adult cohorts became active in early to mid-April followed by bimodal host-seeking activity each year, with the duration and intensity of the first activity period being related to the previous year's summer cohort activity. The first activity peak extended from mid-April through late May and the second activity peak occurred in July. All host-seeking activity ceased by early August, except in 1995, when activity ended on 22 August. Laboratory survival of adults, collected weekly during 1993-1996, was used to estimate the emergence of summer adult cohorts. Summer adult cohorts became active in late May or early June and overlapped with overwintering adult host-seeking activity. The termination of host-seeking activity in overwintering adults could not be determined using the methods employed in this study and is most likely to have continued for the entire season. Host-seeking adults displayed contagious distribution patterns along trails bordering ecotone habitats, as determined by fitting a negative binomial frequency distribution to weekly sampling data. These patterns did not vary from year to year. In addition, the location of D. variabilis activity did not change from year to year, which suggests that microhabitats within apparently homogeneous environments enhance adult survival and lead to 'hot spots' of tick activity despite the ability of vertebrate hosts to disperse D. variabilis populations more widely. These data better define our understanding of D. variabilis adult seasonal and spatial host-seeking activity, estimate for the first time the intensity of summer cohort host-seeking activity, and relate summer cohort activity with spring activity the following year.

Animals↗
PubMed1988

Spatial distribution of motor unit fibers in the cat soleus and tibialis anterior muscles: local interactions.

The spatial distribution of muscle fibers belonging to a motor unit was studied in the soleus and tibialis anterior muscles of adult cats. Motor unit fibers were depleted of their glycogen through repetitive stimulation of the motoneuron or of the functionally isolated motor axon. Subsequently, the position of depleted muscle fibers was mapped on serial cross sections taken along the length of the muscle. A subset of fibers was selected from the cross section containing the largest number of motor unit fibers and 4 spatial analyses were performed. These analyses were designed to determine whether the muscle fibers belonging to a single unit were distributed in a random manner. To test whether the actual distribution was other than random, Monte Carlo techniques were used to simulate the random innervation of a muscle. From these simulations, a test statistic was calculated for comparison with the observed data. Adjacency and nearest-neighbor analyses revealed no tendency for grouping or dispersion of fibers belonging to a motor unit. However, measurement of the distances between all motor unit fibers revealed a greater tendency for grouping than spreading, suggesting the existence of some mechanism that restricts the absolute distribution and territory of a motor unit.

Animals↗
PubMed2005

Determination of spatial distributions of zinc and active biomass in microbial biofilms by two-photon laser scanning microscopy.

The spatial distributions of zinc, a representative transition metal, and active biomass in bacterial biofilms were determined using two-photon laser scanning microscopy (2P-LSM). Application of 2P-LSM permits analysis of thicker biofilms than are amenable to observation with confocal laser scanning microscopy and also provides selective excitation of a smaller focal volume with greater depth localization. Thin Escherichia coli PHL628 biofilms were grown in a minimal mineral salts medium using pyruvate as the carbon and energy source under batch conditions, and thick biofilms were grown in Luria-Bertani medium using a continuous-flow drip system. The biofilms were visualized by 2P-LSM and shown to have heterogeneous structures with dispersed dense cell clusters, rough surfaces, and void spaces. Contrary to homogeneous biofilm model predictions that active biomass would be located predominantly in the outer regions of the biofilm and inactive or dead biomass (biomass debris) in the inner regions, significant active biomass fractions were observed at all depths in biofilms (up to 350 microm) using live/dead fluorescent stains. The active fractions were dependent on biofilm thickness and are attributed to the heterogeneous characteristics of biofilm structures. A zinc-binding fluorochrome (8-hydroxy-5-dimethylsulfoamidoquinoline) was synthesized and used to visualize the spatial location of added Zn within biofilms. Zn was distributed evenly in a thin (12 microm) biofilm but was located only at the surface of thick biofilms, penetrating less than 20 microm after 1 h of exposure. The relatively slow movement of Zn into deeper biofilm layers provides direct evidence in support of the concept that thick biofilms may confer resistance to toxic metal species by binding metals at the biofilm-bulk liquid interface, thereby retarding metal diffusion into the biofilm (G. M. Teitzel and M. R. Park, Appl. Environ. Microbiol. 69:2313-2320, 2003).

Biofilms↗
PubMed1988

Spatial distribution of Ca currents in molluscan neuron cell bodies and regional differences in the strength of inactivation.

The spatial distribution of Ca current in molluscan neuron cell bodies was studied using a large patch method in combination with 2-microelectrode voltage clamp. The method has a spatial resolution equal to about 0.1% of the cell body area. Ca current is not uniformly distributed. The current density varies between patches, changing by as much as a factor of 2.5 over a distance of 20 micron, and there is evidence that Ca current occurs in "hot spots" involving a few hundred channels. The current density increases in a moderately steep gradient from the soma cap, opposite the axon, toward the axon hillock. Ca currents in patches from different regions of the soma are qualitatively different. Currents near the soma cap do not inactivate or inactivate weakly during depolarization, while currents of equal density nearer the axon hillock exhibit pronounced inactivation. The strength of inactivation increases in parallel with the gradient in current density, but local differences in current density, or in the number of active Ca channels, do not explain the variability in inactivation. Inactivating and noninactivating Ca currents could not be distinguished on the basis of activation or deactivation kinetics, voltage dependence of activation, or sensitivity to hyperpolarizing conditioning pulses. Also, the amplitude of noninactivating current near the soma cap is reduced by intracellular Ca injection showing that, like the whole-cell current, Ca current in this region is subject to Ca-dependent inactivation. The data favor the hypothesis that these cells express only one type of Ca channel. Differences in the strength of inactivation may result from local differences in cytoplasmic Ca buffering, local modification of Ca channels in a way that changes their sensitivity to Ca-dependent inactivation, or local differences in the availability of cytoplasmic factors or enzymes that are necessary for inactivation.

Animals↗
PubMed1984

A microcomputer based system for quantifying the spatial distribution of inhaled particles in histological lung sections.

A system is described for quantifying the spatial distribution of inhaled particles in complete lobar histological sections of rodent lung. It is based on a semi-automatic image analyser, linked to a readily available microcomputer. Application of the system to quantify the aggregation of particles, and their distances from airways and lung periphery is described. The observed distributions are compared with the expected distributions from a random set of particles, and the significance of the difference is calculated. Each statistical test is illustrated by an example.

Aerosols↗
PubMed1991

Spatial Distribution of Flavonoid Conjugates in Relation to Glucosyltransferase and Sulfotransferase Activities in Flaveria bidentis.

The spatial distribution of sulfated and glucosylated flavonols as well as of the enzymes involved in the later steps of their biosynthesis, sulfotransferase and glucosyltransferase, were investigated in the shoots of Flaveria bidentis. The highest amounts of both types of flavonoid conjugates (as micromole per gram fresh weight) and the highest activities of their enzymes (as picokat per milligram) were detected in the terminal bud and the first pair of leaves. Sulfotransferase activity was also highest in the upper stem segments and in the basal section of the leaves. Western blot analysis of protein extracts showed that variations in sulfotransferase activity in different tissues correlate well with the amounts of immunodetected enzyme protein. These results were discussed in relation to the possible role of conjugated flavonoids in plant growth.

Journal Article↗
PubMed1987

The spatial distribution of late ventricular potentials.

Body surface potential mapping (BSPM) was used to study the spatial distribution of late ventricular potentials. In a group of 15 normals and 21 patients with documented ventricular tachycardia (VT), BSPM performed with 63 averaged and high-pass filtered ECG leads (LP-BSPM) showed that late potentials have a mostly dipolar distribution and that they can be reasonably well detected with only three orthogonal leads. In a group of 17 VT patients who also had BSPM performed during induced VT (VT-BSPM), six patients had LP-BSPM similar to one of the VT-BSPM, suggesting that the locations and orientations of both types of sources are similar. In a group of 12 VT patients who had epi-endo VT mapping at surgery, LP-BSPM showed close extrema (reflecting antero-apical delay) for patients with anterior or apical VT sites, suggesting that VT originates in delayed regions. BSPM thus provides useful information about the detection and significance of late potentials.

Adult↗
PubMedDate not supplied

Spatial distribution of dialysate in patients and its implications to intradialysate diffusion.

OBJECTIVE: To visualize and quantify the spatial distribution of dialysate in patients on continuous ambulatory peritoneal dialysis (CAPD) and, hence, estimate diffusion times for fluid "pockets" wherever intradialysate concentration gradients may not be dissipated by convective currents. DESIGN: Contrast medium was added to the dialysate of three supine CAPD patients before an exchange prior to computed tomographic (CT) scanning. Spatial information in the CT scanner was then downloaded to other computers and processed to produce impressive three-dimensional models of dialysate distribution using "wire frame technology." RESULTS: Models differed between patients but all demonstrated pooling of dialysate in the paracolic gutters, subphrenic space, and, especially, in the pelvic cavity. Some pockets of fluid were almost isolated. Quantitatively, the models can account for over 80% of the volume of the exchange (2.5 L), displaying an effective area of contact of 913-450 cm2 between parietal peritoneum and dialysate. This amounts to only 11% -21% of the anatomic area, again emphasizing the uneven distribution of dialysate. Ignoring very thin (< 0.1 mm) films of dialysate, the bulk (80%) had mean thicknesses ranging from 1.6 to 1.9 cm. Transcendental equations for bulk diffusion were then applied to these findings to determine a theoretical time for urea of about 2-3 hours to half-saturation, or 5-7 hours to 80% saturation, in the absence of convective currents. CONCLUSIONS: The distribution of dialysate within the peritoneal cavity is very uneven, resulting in long diffusion times in fluid pockets wherever convective currents may be minimal. Hence, intradialysate diffusion should not be ignored when modeling peritoneal dialysis.

Adult↗
PubMed1992

The spread of a parasitic infection in a spatially distributed host population.

Starting from a stochastic model for the spread of a parasitic infection in a spatially distributed host population we describe the way to a continuum formulation by a deterministic model in terms of a nonlinear partial differential equation and an integro-differential equation. The hosts are assumed to occupy fixed spatial positions, whereas the parasites are mobile, however can propagate only within the hosts. To perform the continuum limit we suppose that the size Nh of the host population, the size Np of the parasite population, and the ratio Np/Nh tend to infinity. Accordingly, the parameters determining the time evolution of the host and parasite populations are rescaled suitably.

Cells, Cultured↗
PubMed2006

Spatial distribution of inspiratory drive to the parasternal intercostal muscles in humans.

The human parasternal intercostal muscles are obligatory inspiratory muscles with a diminishing mechanical advantage from cranial to caudal interspaces. This study determined whether inspiratory neural drive to these muscles is graded, and whether this distribution matches regional differences in inspiratory mechanical advantage. To determine the neural drive, intramuscular EMG was recorded from the first to the fifth parasternal intercostals during resting breathing in six subjects. All interspaces showed phasic inspiratory activity but the onset of activity relative to inspiratory flow in the fourth and fifth spaces was delayed compared with that in cranial interspaces. Activity in the first, second and third interspaces commenced, on average, within the first 10% of inspiratory time, and sometimes preceded inspiratory airflow. In contrast, activity in the fourth and fifth interspaces began after an average 33% of inspiratory time. The peak inspiratory discharge frequency of motor units in the first interspace averaged 13.4 +/- 1.0 Hz (mean +/- s.e.m.) and was significantly greater than in all other interspaces, in particular in the fifth space (8.0 +/- 1.0 Hz). Phasic inspiratory activity was sometimes superimposed on tonic activity. In the first interspace, only 3% of units had tonic firing, but this proportion increased to 34% in the fifth space. In five subjects, recordings were also made from the medial and lateral extent of the second parasternal intercostal. Both portions showed phasic inspiratory activity which began within the first 6% of inspiratory time. Motor units from the lateral and medial portions fired at the same peak discharge rate (10.4 +/- 0.7 versus 10.7 +/- 0.6 Hz). These observations indicate that the distribution of neural drive to the parasternal intercostals in humans has a rostrocaudal gradient, but that the drive is uniform along the mediolateral extent of the second interspace. The distribution of inspiratory neural drive to the parasternal intercostals parallels the spatial distribution of inspiratory mechanical advantage, while tonic activity was higher where mechanical advantage was lower.

Adult↗
PubMed1986

The spatial distribution of a blastoderm stage-specific mRNA from the serendipity locus of Drosophila melanogaster.

The spatial distribution of a blastoderm stage-specific mRNA was examined by hybridization in situ to tissue sections of early embryos of Drosophila melanogaster. The mRNA examined, the C mRNA, is coded for by the molecularly-complex locus, serendipity (sry). The C mRNA was found to be expressed in embryos in all nuclei and cells except pole cells, during the syncytial and cellular blastoderm stages and its transcription correlates well with the formation of the cellular blastoderm.

Blastoderm↗
PubMed1976

Spatial distribution of potentials evoked by half-field pattern-reversal and pattern-onset stimuli.

Spatial distributions of visual potentials (VEPs) evoked by half-field checkerboard pattern-reversal and pattern-onset stimuli were studied in 13 subjects, using an 11 lead unipolar array. The main aim was to confirm findings, obtained by previous workers with bipolar recordings, that half-field pattern-reversal VEP's are confined to the contralateral hemisphere and that half-field pattern-onset VEPs are asymmetrical, with greater right hemisphere involvement. Pattern-reversal VEP's contained four consistent peaks, designated here by polarity and peak latency as: (a) P95, positivity contra-lateral and negativity ipsilateral to the field stimulated; (b) P125, predominantly ipsilateral positivity; (c) N165, predominantly ipsilateral negativity; (d) P225; predominantly midline positivity. Pattern-onset VEPs contained three consistent peaks: (a) P125, mainly contraleteral positivity; (B) N175, mainly contralateral negativity; (c) P225, midline positivity. Distributions of pattern-reversal and pattern-onset peaks resembled one another only for P225, suggesting different cortical representation for the other events of the two kinds of VEP. Bipolar pattern-reversal VEPs were largely contralateral, but unipolar recordings showed that this was due to steeper contralateral potential gradients, as ipislateral activity was widespread. Pattern-onset peaks did not differ in amplitude with respect to the half-field stimulated. Previously reported asymmetries were not confirmed. The P125 and N175 pattern-onset peaks were almost entirely restricted to the contralateral hemisphere, but the distributions by half-field were mirror-images of one another. Half-field pattern-onset stimuli could be used to investigate the responsiveness of each hemisphere, although differential hemispheric involvement was not shown. Several differences in amplitude and distribution resulted from varying the width of the vertical central dark strip.

Adolescent↗
PubMed1994

Spatial distribution of back scattering in the nuclear area of the non-cataractous human lens.

The spatial distribution of back scattering from a vertical cross-section of the nuclear area in non-cataractous human lens was investigated. The cross-section was centred on the pupil. There is no significant difference in average nuclear back scattering between sides. The distribution of back scattering along an axis perpendicular to the anatomical axis can be modelled as a second-order polynomial. It is believed that the increase of back scattering in the central region corresponds to the peak protein concentration in the centre of the nucleus. This information was obtained by imaging back scattering with Scheimpflug photography. The back scattering was measured photometrically in a 3 x 10 matrix of measuring areas within the lens nucleus. Each measuring area was 0.20 x 0.20 mm in size. It is anticipated that the established model will allow detection of nuclear cataract with high sensitivity, especially in early stages.

Aged↗
PubMed2002

Spatial distribution and density of prefrontal cortical cells projecting to three sectors of the premotor cortex.

The spatial distribution of prefrontal cortical cells projecting to three different sectors in the premotor cortex was examined. The cells projecting to the three sectors were distributed in separate regions in the dorsolateral prefrontal cortex with a small overlap. Cells projecting to the ventral sector were distributed in the lower bank of the principal sulcus (PS). Those projecting to the restro-dorsal sector were located near the superior limb of the arcuate sulcus, and in the dorsal convexity and upper bank of the PS. Cells projecting to the caudo-dorsal sector were observed in the upper bank of the PS and in the area 8a. These findings suggest that each of the three sectors of the premotor cortex receive different sets of information from the prefrontal cortex.

Amidines↗
PubMed1993

Spatial distribution of excitatory and inhibitory synapses on a Purkinje cell in a rat cerebellar culture.

1. The spatial distribution of excitatory and inhibitory synapses on cultured Purkinje cells was studied with fluorescence, scanning electron microscopy (SEM), and electrophysiological techniques. 2. Presynaptic terminals were identified with immunohistochemical staining of synaptophysin and the results were correlated with SEM micrographs. 3. Excitatory and inhibitory inputs onto the Purkinje cell were identified from the direction and pharmacology of the postsynaptic current. 4. The localization of the presynaptic terminals on the Purkinje cell was observed after electrophysiological identification by filling the presynaptic neuron with Lucifer yellow and the Purkinje cell with Texas red. 5. The axon and presynaptic terminals of excitatory and inhibitory inputs had a different spatial organization. Excitatory inputs from granule cells were exclusively localized on the dendrites of Purkinje cells, whereas inhibitory contacts were found on both the soma and dendrites. This result is similar to that described in vivo.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed2002

Photodynamic therapy creates fluence rate-dependent gradients in the intratumoral spatial distribution of oxygen.

In photodynamic therapy (PDT), treatment efficacy may be reduced by the presence of pre-existing tumor hypoxia or by oxygen depletion during the therapy. Tumor oxygenation during PDT has been measured with needle electrodes, but the intratumoral distribution of this oxygen is not known. In the present study, the spatial distribution of hypoxia during PDT was quantified using the hypoxia-labeling marker EF3. Mice bearing radiation-induced fibrosarcoma tumors were treated with Photofrin-mediated PDT to a total dose of 135 J/cm(2), delivered at a fluence rate of either 75 mW/cm(2) or 38 mW/cm(2). PDT-created hypoxia at each fluence rate was labeled by exposing tumors to EF3 (52 mg/kg) during the period of illumination. Cryosectioning, immunohistochemistry, and fluorescence microscopy were carried out to quantify EF3 binding as a function of distance to the nearest perfused blood vessels in sections cut from within the superficial (light-adjacent) 600 micro m or the deep (light-distant) 600 micro m of tumors (5-6 mm in diameter, approximately 3 mm in depth). In both superficial and deep sections, PDT at 75 mW/cm(2) resulted in the development of significant gradients in tumor hypoxia as a function of distance to a perfused blood vessel. Furthermore, significant hypoxia was detected even in vascular-adjacent tissue. These effects were associated with a significant decrease in the percentage of perfused vessels and a significant increase in the median distance of a cell to the nearest perfused blood vessel. In contrast, during PDT at 38 mW/cm(2), sections from deep tumor levels demonstrated only insignificant increases in the rise in hypoxia as a function of distance to a perfused vessel and in the level of hypoxia in vascular-adjacent tissue. No effects on tumor perfusion were detected during PDT at 38 mW/cm(2). Overall, these results demonstrate that spatially dependent depletion of oxygen can occur during PDT as a function of the fluence rate and that PDT can create significant hypoxia in even tissue adjacent to perfused blood vessels.

Animals↗